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12/16/13
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Chapter 8: Mul3user Radio Communica3ons
Dr. Samir Alghadhban
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Mul3ple-‐Access Techniques
(a) Frequency-‐division mul3ple access
(b) Time-‐division mul3ple access.
(c) Frequency-‐hop mul3ple access.
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Satellite Communica3ons System
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Block Diagram of Transponder
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8.4 Radio Link Analysis
Link Budget is the totaling of all the gains and losses incurred in opera3ng a communica3on link. In par3cular, the balance sheet cons3tu3ng the link budget provides a detailed accoun3ng of three broadly defined items: • Appor3onment of the resources available to the transmiRer and the receiver.
• Sources responsible for the loss of signal power. • Sources of noise.
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8.4 Radio Link Analysis
Where M is the link margin
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Free Space Propaga3on Model
Power Density
Radia3on Intensity
Total Power Radiated
The average power radiated per unit solid angle is
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Direc2ve Gain, Direc2vity, and Power Gain
the direc2ve gain of an antenna, denoted by g(θ, Φ) is defined as the ra2o of the radia2on intensity in that direc2on to the average radiated power
the direc3vity D is the maximum value of the direc3ve gain g(θ, Φ)
Power Gain ( G ) is :
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Friis Free-‐Space Equa2on The received power at distant d is
The path loss, PL, represen3ng signal "aRenua3on" in decibels across the en3re communica3on link, is defined as the difference (in decibels) between the transmiGed signal power Pt and received signal power Pr
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Calcula3ons
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8.5 Wireless Communica3ons The cellular concept relies on two essen3al features, as described here: • Frequency reuse • Cell spliIng
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PROPAGATION EFFECTS
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PROPAGATION EFFECTS
(a) Construc3ve (b) destruc3ve forms of the mul3path phenomenon for sinusoidal signals
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PROPAGATION EFFECTS
Phasor representa3ons of (a) construc3ve (b) destruc3ve forms of mul3path.
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PROPAGATION EFFECTS
Illustra3ng how the envelope fades as two incoming signals combine with different phases.
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PROPAGATION EFFECTS
Experimental record of received signal envelope in an urban area.
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Doppler Shia the incremental change in the path length of the radio wave is
the change in the phase angle of the received signal
The apparent change in frequency, or the Doppler-‐shiJ
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8.7 Binary Signaling over a Rayleigh Fading Channel
The (low-‐pass) complex envelope of the received signal is modeled as follows:
α is a Rayleigh distributed random variable describing the aRenua3on in transmission, Φ is a uniformly distributed random variable describing the phase-‐shia in transmission
The received SNR
For BPSK
The average Pe will be
Where γ is chi-‐square distributed
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8.7 Binary Signaling over a Rayleigh Fading Channel
the mean value of the received signal energy per bit-‐to-‐noise spectral density ra2o
carrying out the integra3on, we get the final result
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8.7 Binary Signaling over a Rayleigh Fading Channel
Performance of binary signaling schemes over a Rayleigh fading channel, shown as con3nuous curves; the dashed curves pertain to a nonfading channel
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8.7 DIVERSITY TECHNIQUES
• Frequency diversity • Time (signal-‐repe33on) diversity • Space diversity
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8.7 DIVERSITY TECHNIQUES
Performance of binary signaling schemes with diversity.
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